Admin-defined taxes for each customers(or customer groups)

Dear Open Cart Community, I have the following issue I would like to address:

I'm working on a college project using OpenCart and there's something I want to try and do.

I'm building a shop for a company that makes kitchen forniture and then sells them to buyers, be it private customers or major chains.
Each one of their furnitures have different price types and each specific customer has a administrator defined tax so to speak.

One example, if I was customer A and I tried buying furniture with price type 3 the total would be something like(note:asterix used as multiplier) this:


Total = item price type 3(40€) * customer defined tax(0.56 or 56%)

This would occour when I tried buying the item(of course, I want that particular tax to be invisible to the user).

Total = 40*0.56 (por example)

The administrator would define which tax would be applied to a specific customer when the administrator approves the customer's account.

Is there any module that allows me to add more fields to the costumer's records? I mean as an administrator it should be possible, can I change the PHP code to add more fields? Or do I need to tweak anything in the Totals module?

I would be thankful for any information you could give me.

Many thanks.